The look of the spots and the season they appear point to the cause, since leaf spot, anthracnose, black spot, and rust each mark leaves differently and at different times. Raking up fallen leaves helps against all four, because the fungi behind them survive the winter on that litter.

Why do leaf spot diseases keep coming back?

Because the fungi overwinter on fallen leaves and spread to new growth in spring. Rain, wind, and humid weather carry spores onto fresh leaves, so a wet spring after a spotty year often brings the problem back.

How can each type of spot be told apart?

By color, position on the leaf, and timing:

• Small brown or black spots on the upper surface, often in early to mid summer: leaf spot
• Light brown dead tissue following the veins in a cool, wet spring: anthracnose
• Round black spots about 1/4 inch to 1 inch across, with yellowing around them, from early to mid spring: black spot
• Small reddish or yellow bumps on the underside, late in the season: rust

When is a fungicide worth using?

When spotting is severe or returns year after year, since ordinary leaf spot rarely needs chemical control. For rust, Liquid Copper Fungicide Spray is applied at spring bud break and twice more at 14 to 20 day intervals, while Fungi Max Multi Purpose Fungicide, a myclobutanil fungicide, is sprayed on trees with anthracnose once signs are first noticed.

Frequently Asked Questions

Does watering affect leaf spots?

Yes. Watering at ground level instead of over the leaves keeps foliage drier during the humid weather these fungi favor.

Can leaf spot diseases spread to branches?

Some can. Anthracnose can form dark lesions and cankers on twigs, so dead or badly diseased branches are pruned out in dry weather, with tools disinfected in 1 part bleach to 4 parts water.

What if the leaves show white powder instead of spots?

That is usually powdery mildew, a different fungal problem. Fungi Max lists powdery mildew among the diseases it controls, alongside anthracnose, leaf spot, and rust.

What if the tree is too tall to spray?

A trunk treatment is the alternative. For trees too tall to reach, TreeHelp's anthracnose guide points to Garden Phos with Pentra Bark, mixed as a concentrated trunk spray.